use std::ffi::c_void;

#[unsafe(no_mangle)]
unsafe fn vbu_realloc_shim(ptr: *mut c_void, new_size: usize) -> *mut c_void {
    if !ptr.is_null() {
        // not supporting proper realloc because it needs bookkeeping and it's unnecessary
        return std::ptr::null_mut();
    }
    let allocation = vec![0u8; new_size].into_boxed_slice();
    Box::into_raw(allocation).cast()
}

#[link(name = "vb")]
unsafe extern "C" {
    #[link_name = "vbuFromISX"]
    fn vbu_from_isx(bytes: *const c_void, length: usize, rom_length: *mut usize) -> *mut c_void;
}

pub fn rom_from_isx(bytes: &[u8]) -> Option<Vec<u8>> {
    if !bytes.starts_with(b"ISX") {
        return None;
    }
    let mut rom_length = 0;
    let raw_rom = unsafe { vbu_from_isx(bytes.as_ptr().cast(), bytes.len(), &mut rom_length) };
    if raw_rom.is_null() {
        return None;
    }
    // SAFETY: the rom was allocated by vbu_realloc_shim, which created it from a Vec<u8>.
    let rom = unsafe { Vec::from_raw_parts(raw_rom.cast(), rom_length, rom_length) };
    Some(rom)
}